Abstract
Fractionation of the bioactive extract of a culture of the marine derived actinomycete Streptomyces cyaneofuscatus M-157 led to the isolation of the known 3-hydroxyquinaldic acid (4), its amide (5) and three new derivatives (1–3) containing different amino acid residues. The structures of the new molecules (1–3), including their absolute configuration, were determined by the analysis of their ESI-TOF MS and one-dimensional (1D) and two-dimensional (2D) NMR spectra and advanced Marfey’s analysis of their hydrolyzation products. Compound 3 spontaneously dimerized in solution to give the disulfide derivative 6. Unfortunately, none of the new compounds isolated confirmed the antimicrobial activity found in the bacterial extract, perhaps indicating that such antibacterial activity might be due to presence in the extract at the trace level of larger bioactive 3-hydroxyquinaldic acid derivatives from which compounds 1–3 are biosynthetic precursors. Cytotoxicity tests confirmed the moderate and weak IC50 values of 15.6 and 51.5 µM for compounds 5 and 1, respectively.
Highlights
Marine actinomycetes continue to be the source of new natural products with interesting bioactive properties
The 16S rDNA of strain M-157 was previously amplified by polymerase chain reaction (PCR) and
The 16S rDNA of strain M-157 was previously amplified by polymerase chain reaction (PCR) and sequenced [13]
Summary
Marine actinomycetes continue to be the source of new natural products with interesting bioactive properties. Depsipeptides containing quinaldic acid moieties in their structures, called chromodepsipeptides, constitute an interesting structural class due to their relevant biological activities These include antibiotics, such as the antibiotics UK-63,052, UK-63,598, and UK-65,662 [1], and their sulfoxide derivatives RK-1355A and B [2], luzopeptins A–C [3,4,5], quinaldopeptin [6] and sandramycin [7,8], or potent cytotoxic agents, such as thiocoraline [9,10] or the structurally related thiochondrilline C [11]. Of this strain identified the presence of 3-hydroquinaldic together with some new structurally Fractionation of this extract using reversed phase flashacid chromatography and HPLC yielded 3related natural products.
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